This invention relates to a holding device for holding a tool or workpiece and more particularly to an expandable tool holding device in which an expansion sleeve is radially expanded to grip a tool or workpiece.
Various types of expandable chucks and arbors are known for clamping a tool on a support member. Known expandable chucks and arbors usually include a thin-walled, expansion sleeve which defines a pressure chamber. A screw and piston arrangement is used to force a fluid into the pressure chamber. The fluid exerts pressure against the thin-walled expansion sleeve causing it to expand radially to grip the tool or workpiece. Examples of these types of devices are shown in U.S. Pat. Nos. 4,387,906 and 4,677,792.
Another type of expandable chuck which is known is the shrink-fit chuck. In a shrink fit chuck, the tool shank is made slightly larger than the opening in the chuck. The chuck is heated to cause expansion of the opening sufficient to permit insertion of the tool. Once the tool is inserted, the chuck is allowed to cool. As the chuck cools, it contracts to grip the tool shank.
Both fluid expandable chucks and shrink fit chucks are able to achieve accurate and repeatable positioning of the tool or workpiece. Additionally, both have excellent gripping capabilities. Shrink-fit chucks also provide excellent rigidity, whereas fluid expandable chucks are only average in this respect. However, both shrink-fit chucks and fluid expandable chucks have significant drawbacks.
Fluid expandable chucks are generally large and cumbersome. Also, they are susceptible to leakage during operation which makes them less reliable than other chucking devices. The primary disadvantage of shrink-fit chucks is that they can be difficult to use. For instance, it is sometimes difficult to remove a tool from the chuck since heating the chuck causes the tool to be heated by conduction as well. Moreover, relatively high temperatures are needed in order to effect sufficient expansion of the chuck to remove the tool.